The present invention relates to a data generating method and a data generating apparatus which can enhance an error correction capability without degrading a formatting efficiency when high-density recording is performed in a digital record/playback apparatus using an optical disk, etc.
In a digital record/playback apparatus for recording/playing back digital data on/from an optical disk, a magnetic disk, magnetic tape, etc., a recording capacity per unit area has been increased with the development of high-density recording technology. On the other hand, in the digital record/playback apparatus, in order to cope with the problem of data errors due to noise or flaws on the medium, error correction coding is performed on the record data so that errors can be corrected.
If the recording density increases, the error rate also increases due to a decrease in signal components. Moreover, even if a flaw equal in size to one on an ordinary medium occurs on the high-density recording medium, more errors will occur than on the ordinary medium. Thus, the high-density recording medium requires error correction codes with a higher error correction capability. In particular, as the signal output decreases, it becomes more important to cope with the problem of random errors.
An example of the error correction code generally used in modern digital record/playback apparatuses is a product code formed by combining two kinds of Reed-Solomon codes. The product code comprises inner codes, which are successive or concentrated in a narrow range in a recorded data stream, and outer codes arranged in an interlaced fashion in the recorded data stream. An example of the product code is shown in FIG. 8.
Record data is arranged in a two-dimensional block. In FIG. 8, outer codes are encoded vertically for each column. An outer code parity generated by the coding is located at a lower end of each column. Then, inner codes are encoded horizontally for each row of the data and outer code parity. The inner code parity generated by the encoding is situated at a right end of each row. The product code block thus encoded by the outer codes and inner codes is taken out and successively recorded on a recording medium along with sync patterns for identifying delimiters of data.
When the data thus recorded is played back, the product code block shown in FIG. 8 is reconstructed from the read-out data, and inner code correction is performed by using the inner code parity for each row. Then, outer code correction is performed by using the outer code parity for each column.
The inner code correction is effective mainly for correction of random errors. If a burst error occurs due to a flaw on the recording medium, errors concentrate at one inner code. Thus, the burst error cannot effectively be corrected in the inner code.
The outer code correction is effective mainly for correction of burst errors. Since most of random errors are eliminated by the inner code correction, it is considered that most of errors corrected by the outer code correction are burst errors. The outer codes are arranged in the column direction in the product code block, and thus even if successive burst errors have occurred, it is less possible that many data units are made erroneous at a time. Accordingly, the burst errors, which have not been corrected by the inner code correction, can be corrected by the outer code correction.
The recording density of the medium increases gradually as the capacity of the storage device increases. If the recording density increases, the area of the medium which can be used for storing unit data decreases and the output level of the read-out signal decreases. The decrease in the read-out signal level increases the number of random errors. In order to compensate the decrease in the signal output level, the performance of the medium has been improved. Nevertheless, the random error rate has increased.
Accordingly, when the high-density recording is performed, it is necessary to use error correction codes having a higher random error correction capability. In the product codes, the random error correction capability depends greatly on the contribution of the inner code correction capability. It thus appears that the enhancement of the inner code correction capability is effective to increase the random error correction capability.
A method of increasing the parity data to be added by means of coding is adopted to increase the correction performance of Reed-Solomon codes. However, if the inner code parity is simply increased, the effective data ratio (formatting efficiency) per unit record data will decrease. Even if the error correction capability is increased by the addition of the inner code parity and the increased capability is used to enhance the recording density, the record data amount decreases due to the decrease in formatting efficiency.
As has been described above, even if the random error correction capability is increased by increasing the inner code parity data in the conventional method, the formatting efficiency decreases and the effect of improving the memory capacity in the apparatus decreases.
The present invention aims at providing a data generation method and a data generation apparatus capable of enhancing recording density by increasing an inner code party number without lowering formatting efficiency.
According to the invention there is provided a data generation method for generating a data stream comprising the steps of: a first data generation process for recording data on a recording medium with a first recording density including, encoding input digital data in accordance with a first error correction coding to generate a first check parity, making a first unit block having a data area having a predetermined data length and the first check parity provided at an end of the data area, dividing first the unit block into a plurality of divided areas, and providing a sync pattern at a head of each of the first divided areas to obtain a first data stream, and a second data generation process for recording data on a recording medium with a second recording density higher than the first recording density including, encoding input digital data in accordance with a second error correction coding to generate a second check parity greater in number than the first check parity, making a second unit block having a data area having a predetermined data length and the second check parity provided at an end of the data area, and providing a sync pattern at a head of the second unit block to obtain a second data stream, and wherein at least one of the first data generation process and the second data generation process is used to generate the data stream.
According to the invention there is provided a data generation method for generating a data stream comprising the steps of: a first data generation process for recording data on a recording medium with a first recording density including, encoding input digital data in accordance with a first error correction coding to generate a first check parity, making a first unit block having a data area having a predetermined data length and the first check parity provided at an end of the data area, dividing the first unit block into a plurality of divided areas, and providing a sync pattern at a head of each of the first divided areas, to obtain a first data stream, and a second data generation process for recording data on a recording medium with a second recording density higher than the first recording density, encoding input digital data in accordance with a second error correction coding to generate a second check parity greater in number than the first check parity, making a second unit block having a data area having a predetermined data length and a part of the second check parity provided at an end of the data area, dividing the second unit block into a plurality of second divided areas, and providing a sync pattern at a head of a top one of the second divided areas, and providing a remaining part of the second check parity at a head of another one of the second divided areas which follows the top one, to obtain a second data stream, and wherein at least one of the first data generation process and the second data generation process is used to generate the data stream.
According to the invention there is provided a data generation apparatus for generating a data stream comprising: a first data generation unit which records data on a recording medium with a first recording density including, a first encoder which encodes input digital data in accordance with a first error correction coding to generate a first check parity, a first unit block making section which makes a first unit block having a data area having a predetermined data length and the first check parity provided at an end of the data area, a first dividing section which divides the first unit block into a plurality of divided areas, and a first providing section which provides a sync pattern at a head of each of the first divided areas to obtain a first data stream, and a second data generation unit which records data on a recording medium with a second recording density higher than the first recording density including, a second encoder which encodes input digital data in accordance with a second error correction coding to generate a second check parity greater in number than the first check parity, a second unit block making section which makes a second unit block having a data area having a predetermined data length and the second check parity provided at an end of the data area, and a second providing section which provides a sync pattern at a head of the second unit block to obtain a second data stream, and wherein at least one of the first data generation unit and the second data generation unit is used to generate the data stream.
According to the invention there is provided a data generation apparatus for generating a data stream comprising: a first data generation unit which records data on a recording medium with a first recording density including, a first encoder which encodes input digital data in accordance with a first error correction coding to generate a first check parity, a first unit block making section which makes a first unit block having a data area having a predetermined data length and the first check parity provided at an end of the data area, a first dividing section which divides the first unit block into a plurality of divided areas, and a first providing section which provides a sync pattern at a head of each of the first divided areas, to obtain a first data stream, and a second data generation unit which records data on a recording medium with a second recording density higher than the first recording density, a second encoder which encodes input digital data in accordance with a second error correction coding to generate a second check parity greater in number than the first check parity, a second unit block making section which makes a second unit block having a data area having a predetermined data length and a part of the second check parity provided at an end of the data area, a second dividing section which divides the second unit block into a plurality of second divided areas, and a second providing section which provides a sync pattern at a head of a top one of the second divided areas, and a third providing section which provides a remaining part of the second check parity at a head of another one of the second divided areas which follows the top one, to obtain a second data stream, and wherein at least one of the first data generation unit and the second data generation unit is used to generate the data stream.
According to the present invention, when recording density is high, the size of a block to which a sync pattern is added is made greater than in the case of low recording density. Thus, the number of sync patterns per unit data is reduced and additional check parity is assigned to a region corresponding to the omitted sync pattern. Thereby, the error correction capability at the time of high density recording can be enhanced without lowering the formatting efficiency.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.